In early April of last year, a Mexican government worker named Adela María Gutiérrez fell ill. Wracked by fever, aches and lethargy, Gutiérrez thought she was suffering from a very bad cold and acted accordingly, treating herself with aspirin, moist towels and bed rest. A local clinic gave her antibiotics. Nothing worked.

Finally, after a week, Gutiérrez sought help at the General Hospital in the city of Oaxaca. She felt listless and struggled to breathe. Her limbs were blue from a lack of oxygen. A lab test revealed a viral infection, but it was a flu bug doctors had not seen before. They began treatment. Nothing worked. Gutiérrez died on April 13, 2009. She was 39, the first known fatality caused by a new strain of influenza called H1N1.

On the same day Gutiérrez died, the U.S. Centers for Disease Control and Prevention learned of a similar case involving a 10-year-old boy in San Diego County, also infected with an unidentified respiratory illness. A second case in Imperial County appeared four days later. These were the first known U.S. cases of H1N1.

The boy and girl recovered. More alarming to health authorities was how fast the virus was spreading. Within a week, there would be confirmed H1N1 cases scattered across the United States, Europe and Asia. These would multiply like, well, a virus. On June 11 — just 58 days after Gutiérrez’s death — the World Health Organization declared that H1N1 had reached “pandemic” status. The virus had gone global.

Fear of a new killer flu gripped the world, especially because the virus appeared deadliest to the young and strong. There were emergency conferences and international proclamations. Impacted cities temporarily shut down. Schools closed. The media blared warnings and cautionary tales, often alluding to earlier influenza scourges: the 1968-69 pandemic in which 1 million people died worldwide; the 1957-58 pandemic that killed almost 2 million; and, worst of all, the 1918-19 pandemic in which an estimated 50 million people perished around the world.

Of course, the 2009-10 version of the H1N1 flu virus has proved to be not nearly so virulent and deadly. According to the WHO, the current confirmed worldwide death toll from H1N1 is 17,798 — less than half of the oft-cited figure that 36,000 people in the United States die each year from causes related to seasonal flus.

“We dodged a bullet,” said Sumit Chanda, an infectious disease researcher at the Sanford/Burnham Medical Research Institute in La Jolla.

But the gun remains loaded.

The 2009-10 flu season is basically over (at least in the Northern Hemisphere), but the bug will be back. The current strain — or a new, mutated version — will return when the next flu season begins in late fall. We asked local experts — scientists, doctors and public health officials — to take stock of H1N1, of what happened — and what did not; what was learned and what remains to be discovered — and done.

What have we learned about H1N1 that we didn’t know a year ago?

A year ago, we knew H1N1/2009 was highly contagious. We did not know how virulent or deadly it would be. We did not know whether it would mutate into something even more deadly. We have learned that for most people, the disease is mild, similar to seasonal flus. But for a small minority, the disease becomes severe very quickly.

— Robert Liddington

Director, Infectious Disease Program

Sanford/Burnham Medical Research Institute

We learned that H1N1 is a particular problem for children and young adults, especially pregnant women. So H1N1 is “mild,” unless you are a child or young adult. We saw twice as many pediatric deaths in the U.S. last year compared with the average.

— Dr. Mark Sawyer

Professor of clinical pediatrics, University of California San Diego School of Medicine

The swine-origin H1N1 that emerged last year is very different antigenically from the same H1N1 subtype that has been circulating as seasonal flu and in the seasonal vaccine. What we have learned in the last year relates to how “novel” influenza viruses can re-emerge from avian and pig reservoirs when general immunity in the human population wanes to strains and subtypes that have appeared as previous pandemics.

Hence “old” viruses can make the jump from birds and pigs back into humans.

— Ian Wilson

Professor of structural biology, The Scripps Research Institute

Were any discoveries particularly surprising?

The fact that this influenza strain did not have the gene for “severity” was surprising, but welcome. The increased risk of complications and death for pregnant and postpartum women, and the risk for obese and morbidly obese individuals, were not generally recognized before the H1N1 outbreak.

— Dr. Wilma Wooten

Public Health Officer, San Diego County

The fact that most people responded to one dose of the vaccine was a surprise. Since H1N1 was a very different strain than previously circulating ones, we didn’t expect people’s immune systems would recognize it, but they did. That was a huge benefit since we only had to get one dose of vaccine into most people to protect the community.

— Sawyer

The big surprise was that those of us in the “mature years” category retained residual immunity from our exposure to influenza before 1950 or so. The result was that the age group that (usually) experiences the highest mortality rates was relatively protected. The morbidity and mortality in younger folks was substantial and merited the concern, but the magnitude of the overall morbidity and mortality was dampened by the natural protection of older folks.

— Dr. Douglas Richman

Professor of pathology and medicine, University of California San Diego, VA San Diego Healthcare System

In retrospect, was talk of a pandemic justified?

Influenza remains an unpredictable disease. While this H1N1 strain was less virulent overall, we know that influenza viruses are constantly changing and a newly formed virus strain could result in widespread serious illness. The question was when, not if.

— Wooten

People who doubt that this was a pandemic are confused about what a pandemic is. It’s a worldwide epidemic. This infection spread around the world in record time — a testimony to the global nature of infections in the 21st century. Not only do people fly halfway around the world in a day, they bring their infections with them. There is hardly a person on the planet who doesn’t know someone who had H1N1 infection (although they may not know they had it). This was a pandemic, and the early declaration that it was was right on.

— Sawyer

The term pandemic has to do with the geographic spread of a disease and not with the severity. So, use of the term was completely appropriate and justified last year and now. Unfortunately, there was (and still is) a lot of misunderstanding as to this term, and it caused a significant degree of worry and concern.

How would you grade the performance of public health officials and agencies?

The overall response, mostly coordinated through public health agencies, was outstanding. Governmental institutions demonstrated flexibility and quick decision-making, neither of which are typical attributes of governmental responses. Those who question the value of public health agencies need to imagine what this pandemic would have been like without the CDC and local health-department responses. There would have been widespread paranoia and panic. There would not have been a vaccine. We wouldn’t know if the virus responded to antiviral drugs. We wouldn’t have had a test for the virus. Many more people would have died.

— Sawyer

The response was remarkably efficient. Within weeks of the outbreak, global awareness was raised, “Patient Zero” was identified and circulating strains of virus were quickly made available to scientists for characterization and vaccine development.

There was a worldwide pandemic, so the warnings were definitely justified. Viruses are unpredictable, especially when they spread through the population rapidly, and are capable of acquiring mutations. Whenever a pathogen jumps species and shows signs of efficient human to human transmission, we will need to sound the alarm.

However, this event also exposed weakness in our response, particularly around vaccine production and distribution. We will need to invest in approaches to accelerate vaccine production and increase vaccine efficiencies, so less vaccine can be used to immunize more people. Of particular concern is the distribution of vaccine in underdeveloped regions of the world.

All health-care facilities are required to have pandemic influenza planning and the necessary protocols in place. Strategies to prevent transmission of infection, such as source control, respiratory hygiene and cough etiquette, hand hygiene, personal protective equipment and the importance of influenza vaccination, are promoted year-round. As the pandemic unfolded, however, it became evident that although such recommendations are in place, the practical application of such strategies requires consistent reminding.

— Dr. Raymond Chinn

Infectious disease specialist/epidemiologist, Sharp Memorial Hospital

The response was exceptional, though we were probably lucky this time.

When assessing the response of public health authorities, it is important to consider the potential ramifications of a more conservative approach. Rapid decisions of this sort will always have to be made on the basis of incomplete information or data, before we have a sense of just how deadly a virus may be. If we had waited longer before reacting and the virus had been significantly more virulent, the severity of the pandemic and the number of deaths could have been astronomical. This must always be weighed against the risk of causing unnecessary alarm.

In addition, when the system works well and dangers are averted or minimized, people are more likely to question whether the actions taken were justified since it is difficult to predict the outcome in the absence of intervention. In this case, it is clear that the actions taken in response to the “swine flu” outbreak saved lives and prevented numerous infections, though it would be impossible to speculate on the exact numbers.

— Wilson

How would you grade media coverage?

Generally well. The media continued to emphasize the importance of this pandemic even after the initial excitement. Early on, there was too much focus on the numbers — the body counts, if you will. I think that may have thrown off the public perception of how widespread H1N1 was since most cases were not tested and therefore didn’t end up in the counts.

— Sawyer

One criticism I would have is that it could have been better explained that the actions taken are aimed to prepare for a worst-case scenario, not that a worst-case scenario was certain. Some media organizations were guilty of this and seemed to have little interest in communicating a more complicated story, especially in the first months of the outbreak. There were other media outlets, however, that did a good job of providing detail, facts and perspective on the H1N1 situation.

The media did OK, but I do have one very big bone to pick. The media likes controversy and generally presents the truth as somewhere in the middle of two positions. I find that when it comes to vaccines in general, (the media caters) to the scientifically ignorant and plays into the dangerous implantation of public health practices. It’s like saying the truth is somewhere between intelligent design and evolution. There are solid, proven facts about the efficacy and risks of most vaccines, including influenza. If the media is to present the truth and facts, then a “balance” between the two sides is not informed or appropriate.

— Richman

What about the public response?

Unfortunately, not enough people acted on the adage “An ounce of prevention is worth a pound of cure.” Only one-third of the population was immunized. Less than half of pregnant women were immunized. Nonimmunized pregnant women were dying well after vaccine was widely available. People kept going to work when they were sick, thus exposing their friends and co-workers to H1N1. The response to a pandemic like this requires a total community effort, like the kind we saw after 9/11 or Hurricane Katrina.

— Sawyer

The public response was commendable, for the most part. People reacted pragmatically and responsibly, taking appropriate measures (vaccinations, staying home when sick, hand washing) without panicking. However, after the H1N1 and SARS scares failed to materialize into high mortality pandemics (thankfully), there is a real fear that the public may become desensitized to future warnings and fail to remain vigilant. It is always important to keep in the back of our minds that the next deadly pandemic may only be a plane flight away.

— Chanda

I think there was some fear and confusion among the general public despite good efforts on the part of the public health community to deliver accurate and timely information. I think that gets to a larger issue of how we, as a society, need to collectively come to grips with how to most effectively disseminate information in these types of public health emergencies.

— Sette

What’s the take-away lesson from this virus and this flu season? What should we be thinking about or doing before the next flu season or for the future?

Safe, rapid and efficient production of more potent vaccines — and ensuring their worldwide distribution — is the most effective way to diminish the global health impact of another influenza pandemic. Investments must be made to promote these efforts, as well as educating the public of the benefits of vaccination. Particular emphasis should be paid to address the current concerns and misinformation surrounding vaccination risks, so that people can make an informed choice on whether to vaccinating themselves and their children.

— Chanda

The experience showed that while the production of the H1N1 vaccine was rapid, relatively speaking, the ability to quickly produce vaccines is still suboptimal. A better scientific understanding of what makes influenza strains dangerous is necessary. There will always be a lag time between discovery of a new strain and having the epidemiologic data on how much harm it does in humans. This lag phase should be bridged by testing the damage the virus does in appropriate model systems.

— Peters

The H1N1 situation exemplifies how society is vulnerable to new infections, as previously noted in the case of SARS and avian flu. While H1N1 turned out to be much milder than feared, it emphasizes the importance of continued vigilance and intensive research efforts to battle infectious disease.

It is also apparent that, in some cases, the secondary damage to society caused by fear and panic exceeded the actual damage to society caused by the disease itself. This issue is relevant in the context of the need for our society to collectively come to grips with how to most effectively deal with these types of public health emergencies.

— Sette

Flu is forever. The flu virus biology predicts that we will continue to see annual epidemics of flu and periodic pandemics when new strains arise. We need to increase our efforts to protect the community. Beginning this fall, the recommendations for influenza vaccine are that everybody, every year, needs an influenza vaccine. All adults, all children, all pregnant women, all seniors, all adolescents, all health-care workers, all teachers. Everybody.